The present invention relates to a method and device for winding a web in a paper machine.
With respect to the prior art related to the present invention, reference can be made. to the applicant""s FI Patent Application 942451, in which a. method and a device in winding of a web, are described. In said method, a web is wound onto, a spool on support of a support roll while the web is passed through a. nip formed between the support roll and the roll that is being produced. In the method, the spool is supported at least partly, and the spool/roll is supported and/or loaded by means of a device whose position can be shifted. In the method, in the initial stages of winding, the loading/support unit/units in said device is/are shifted substantially in a plane passing through the axes of the support roll and of the roll that is being produced as a linear movement so as to load and/or to support the roll that is being produced the winding position. When the winding makes progress, the loadmg/support unit/units of the device is/are shifted downwards along a path substantially parallel to the circumference of the roll, and, in the final stage of winding the roll that is being completed is supported from below by means of said unit.
On the other hand, in the device in accordance with said FI Patent Application No. 942451, the web is wound onto. a spool while supported by a roll and while passed through a nip formed between the support roll and the roll that is being produced. Said spool is at least partly supported by means of a support device fitted in the centre of the spool. Further, the device comprises a unit for supporting the spool and for loading the roll. Said unit has been fitted as a combined loading/supporting and surface-drive member. The device also comprises members, for shifting the unit substantially in a plane passing through the axes of the support roll and of the roll that is being produced. as a linear movement, on one hand, and substantially along a curved path in the direction of the circumference of the roll, on the other hand.
In the applicant""s Finnish patent application xe2x80x9cDevice in winding of a webxe2x80x9d, to be filed on the same day with the present patent application, a solution is described in which an improvement is suggested for the applicant""s said FI Patent Application 942451. In said suggestion of improvement, the rolls of the loading/support and surface-drive member have been coupled together by means of coupling members so that movements of the rolls in relation to one another are geometrically positively controlled.
With respect to the prior art related to the present invention, reference is made to the publication U.S. Pat. No. 4,883,233, which discloses a method and device in winding a web onto a spool for forming a web roll and comprising a support roll, a rider roll unit with two rider rolls and a rider belt and means for supporting the spool. Further, there are disclosed means for measuring a force applied by the rider roll unit to the web roll.
With respect to the prior art related to the present invention, reference can also be made to the published DE Patent Application 3737503, in which a rigid rider roll unit connected with a reel slitter machine is described, whose loading is based on loading by means of a rocker arm. By means of this prior-art arrangement, the factual effective forces cannot be found out, nor has an arrangement for regulation of the load been suggested in it.
It is a common problem of the prior-art devices mentioned above that the force that is applied by the rider roll/set of rider rolls to the roll that is being formed is not known sufficiently precisely. This force is, as a rule, measured from some articulated joint in the support structure of the rider roll unit. Then, from this measured value, by means of various approximations, the force applied by the rider roll to the web roll is computed. Since the construction of articulated joints that supports the rider roll unit always involves a play and since the relative positions of the articulated arms in the construction of articulated joints are changed when the rider roll unit is shifted to different positions, the result of the computing is unavoidably inaccurate. The error is increased by the fact that the prior-art force measurement detectors measure the force in one fixed direction, in which case, since the direction of the effective force is varied when the support structure moves, the change in direction must be taken into account when the measured signal is processed.
A second factor that causes an error in the measurement of force when the measurement is made from some articulated joint of the articulation structure that supports the rider roll unit is the weight of the rider roll unit and of the articulation structure that supports the unit. The weight of the rider roll unit and of the articulation structure that supports the unit is considerable in comparison to the linear load that is aimed at between the rider roll unit and the roll that is being formed. Further, in such measurement, it must be taken into account that the force applied by the weight of the rider roll unit to the roll varies along with the position of the rider roll unit. Thus, out of the measurement results. it would be necessary to be able to separate the errors arising from said factors, but this is difficult in practice.
Further, the measurement mentioned above, in which the force applied by the rider roll to the web roll is measured from some articulated joint in the articulation structure that supports the rider roll unit, involves the drawback that by its means it is impossible to find out the distribution of the force between the rolls in the rider roll unit. When the rider roll unit is attached rigidly to its pivot arms, very precise positioning devices are needed to align the roll/set of rolls against the web roll in the desired way. In particular, when two rolls are employed., even a little error in the position has the consequence that one of the rolls presses the web roll with a greater force than the other one, i.e. the load is not symmetric. In such a case, at the maximum, a higher linear force is applied to the web roll than if both rider rolls loaded the web roll with equal forces, which has an effect on the structure of the roll that is formed.
The object of the present invention is to suggest a method and a device in relation to winding, in which method and device it is possible to measure precisely the factual forces between the rolls of the rider roll- unit and the roll that is being formed and, thereby, to provide regulation of load and/or regulation of position.
In the solution in accordance with the invention; the winding head of the rider roll unit is provided with a detector or detectors, by whose means the nip force between the rolls of the rider roll unit and the roll that is being formed and/or the distribution of the nip force can be measured. Based on the measurement result received from the detectors, the logic determines the regulation parameters for the loading and/or positioning means, in which connection it is possible to regulate the force of contact of the rider roll unit precisely in the direction of the radius of the web roll by means of a feedback-connected regulation. Further, by means of the detectors, the contact forces of each roll are found out separately, which permits an overall control of the profile of nip contact between the rolls during winding. If the rolls load the web roll unevenly because of a somewhat incorrect position of a rigid set of rolls, the situation is amended by running the set of rolls into a correct position, based on the measurement results that have been obtained.
As the detectors are placed in the winding head of the rider roll unit, they are placed as close to the contact point between the rolls of the rider roll unit and the roll that is being formed as possible, in which case the factual nip load between the rolls and the web roll and the distribution of said load are transmitted to the detectors. The more accurate measurement of the forces between the rider roll unit and the web roll has again the consequence that the regulations of the rider roll unit are carried out based on the factual situation prevailing in the web roll, and in this way it is possible to form better rolls, i.e. the quality of winding is improved.
In the present invention, the measurement of the force always takes place in the direction of the straight line passing through the centre point of the straight line that interconnects the centres of the rider rolls and through the centre point of the roll that is being formed. This is why the measurement always gives a correct result irrespective of the position in which the rider roll unit is placed on the face of the web roll.
When no drive has been switched on in the roll or rolls of the rider roll unit, the force measured from the winding head of the rider roll unit is directly the force applied by the rider roll unit to the web roll. If the drive has been switched on in the rider roll or rolls, a surface drive is applied by the belt that surrounds the rider rolls to the roll that is being formed. This surface drive again causes a torque in the winding head, which torque is seen in the force measurements. The torque produced by this surface drive can be determined from the power taken by the drive motors of the roll or rolls, and it can be taken into account in the measurement results.
When the rider roll unit is used at the side of the web roll and for supporting the web roll, the distribution of load is regulated by regulating the vertical position of the rider roll unit so that the desired distribution of load is accomplished between the rolls, which distribution is measured and regulated by means of the detectors.